Field emission devices, and addressable matrices of field emission devices, are known in the art. Selectively addressable arrays of field emission devices are used in, for example, field emission displays. These devices include extraction electrodes (gates) formed on a dielectric for selectively addressing the field emitters, such as Spindt-tip field emitters. It is known in the prior art that the material of the extraction electrodes differs from that of the field emitters and that the Spindt-tip field emitters are treated to provide a sharper tip which increases the local electric field strength at the electron emission tip, thereby reducing voltage requirements. Because the material comprising the extraction electrodes differs from the material comprising the field emitter, it is possible to choose a sharpening etchant which selectively etches the field emitter tip while being inert to the extraction electrode. For example, it is known to make the Spindt-tip field emitters from niobium and molybdenum, wherein the upper, tip portion includes the molybdenum. Prior to the cone deposition, the extraction electrodes, which are made from niobium, are patterned on the dielectric. A parting layer of nickel is then formed on the niobium. After the deposition of the molybdenum Spindt-tip field emitters in emitter wells formed in the dielectric, the excess emitter material is removed by selectively etching the parting layer, upon which the excess emitter material is disposed. Thereafter, the tips of the field emitters are sharpened using an oxygen plasma followed by an SF.sub.6 plasma, to which the extraction electrodes are inert. However, this prior art scheme is not suitable for use in configurations wherein the material comprising the extraction electrode is the same as the material comprising the field emitter tip; an etchant with respect to the field emitter tip is thereby also an etchant with respect to the extraction electrode.
It is also known in the art to coat field emitters with a material which enhances field emission of electrons therefrom and field emission stability. These coating schemes have only been performed on non-addressable arrays. A tip coating process for an addressable array of field emitters, however, must preserve the electrical isolation between individual extraction electrodes. Tip coating materials in the art include gold and diamond. These efforts have not addressed methods for selectively depositing the coating materials on the tips while preventing their deposition in the regions between individual extraction electrodes. Prior art coating schemes have involved only single tips or simultaneously addressable arrays of tips. Conductive coating materials not adequately removed from the regions between individual extraction electrodes of selectively addressable arrays would destroy electrical isolation therebetween, thereby not realizing addressability of the array.
Thus, there exists a need for a method for shaping and coating Spindt-type field emitters which preserves the integrity of, and electrical isolation between, the extraction electrodes.